Strong British prime ministers, such as Margaret Thatcher, Harold Macmillan and Tony Blair – to the frustration of Whitehall and the Foreign Office – frequently commandeered UK foreign policy, leading to inevitable inquests about the mistakes made owing to either secretive or informal policy-making.

David Cameron tried to rectify the danger of disjointed government by establishing the National Security Council, a formalisation of the Whitehall foreign policy process.

But ever since Theresa May became prime minister, and all foreign policy oxygen was sucked up by Brexit, a new problem has emerged – the absence of a strong No 10 hand on the wider foreign-policy tiller.

It has left two Eurosceptics, the foreign secretary Boris Johnson, and the international development secretary, Priti Patel, with an unusual amount of latitude. Patel has filled the void with her own freelance policy towards the Middle East while Johnson has struggled to grip a coherent foreign policy. One arguably has known her own mind too well. The other not well enough. Both have a poor relationship with accuracy.

Priti Patel wanted to send aid money to Israeli army, No 10 confirms

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Their collective, if differing mistakes, not only weaken the Eurosceptic cause, but also add to the impression of a country, in foreign policy terms, adrift in the mid-Atlantic. The mistakes are all the worse because they concern the Middle East at a time when the area is close to the brink of a Saudi-Iranian war, and the Iranian nuclear deal, prized by the UK, is under siege.

The case of Patel is the most egregious. Her failure to inform the UK ambassador to Israel, the Foreign Office, or No 10 of her plan to see the Israeli prime minister, Benjamin Netanyahu, on her August holiday to Israel is quite extraordinary. A former vice-chair of Conservative Friends of Israel, she discussed with the Israeli prime minister his plans for a meeting with Mrs May on the anniversary of the Balfour declaration, but then failed to pass on this discussion to No 10 itself, raising questions about where her ultimate loyalty lies.

Even when May met Netanyahu on Thursday last week, she had no knowledge of Patel’s freelance meeting, even though Patel had told an embassy official about them on 24 August, after the meetings occurred. It is not clear how much Department for International Development officials were informed, or whether Patel failed to tell the full truth, in the same way that she misled the Guardian last Friday.

This is not just a matter of good manners or Whitehall box-ticking. Liam Fox, after all, was forced to resign as David Cameron’s defence secretary when it was discovered he was running a freelance defence policy.

Lord Ricketts, the former national security adviser, stresses: “It is not just about a breach of the ministerial code. The rules and convention exist for a reason, and the reason is that you need to have a coherent presentation of Britain’s foreign policy to each country, and if different ministers go without consultation and without briefing, there is a risk of confusion.” There are few more contested, or sensitive areas of British foreign policy than its policy towards Palestine, or indeed Iran.

At stake are two specific issues – the strength of Britain’s support for a two-state solution in the Middle East, including the role of Israeli occupation, and concerns that UK’s £54m aid programme in Palestine needs to be curbed.

Patel, in public, has always stuck to the official Foreign Office support for the continued feasibility of a two-state solution, but ever since January last year she has been agitating to redirect DfID’s Palestinian aid programme.

In October last year, it was even reported that Patel had suspended £25m in funds to Palestine pending an investigation, a report that was subsequently denied.

Israeli critics fear the UK aid budget is going indirectly or directly to help Palestinian prisoners, dubious NGOs or to fund school textbooks that incite religious hate. Patel has repeatedly promised to stop money going to the wrong people. In July, a month before her visit, British Israeli groups successfully lobbied for £3m to be redirected to co-existence programmes, a funding stream dedicated to people-to-people reconciliation.

Quick guide

Boris Johnson's errors of judgment

Nazanin Zaghari-Ratcliffe

Boris Johnson said that the British-Iranian citizen Nazanin Zaghari-Ratcliffe, convicted of spying in Iran, was “simply teaching people journalism” – a statement her family and her employer both said was untrue. His comments were subsequently cited as proof that she was engaged in “propaganda against the regime”.

'Dead bodies'

After Johnson suggested that the Libyan city of Sirte might become a new Dubai once “the dead bodies” were removed, Downing Street said it was not “an appropriate choice of words”.

Johnson apologised after causing a “livid” reaction in a worshipper in a Sikh temple in Bristol by discussing his enthusiasm for ending tariffs on whisky traded between the UK and India. Alcohol is forbidden under some Sikh teachings.

Continental drift

Boris Johnson referred to Africa as “that country” in his Conservative party conference speech.

On her visit in the summer – in which she never visited occupied Palestine – she heard from Netanyahu how the Israel Defence Forces based in the occupied Golan Heights was providing aid to Syrian refugees coming over the border. To ask officials if the UK could support this programme showed an ignorance that the UK did not recognise Israel’s occupation of the Golan Heights, or that Israel was a minor combatant in Syria.

Boris Johnson’s error is less deliberate, but equally worrying, since it plays to a character fault. No one doubts his intelligence, his fascination with foreign policy or optimism about Britain post-Brexit. But in diplomacy, as successive former foreign secretaries advised today, words, tone and mind-numbing grip of policy detail matters. In this business, as the former Labour foreign secretary Jack Straw said, “careless talk can cost lives”, or even extended prison sentences. He is head of MI6, but his performance is hardly going to encourage the intelligence services to divulge to him its deepest secrets.

In his defence in the case of Nazanin Zaghari-Ratcliffe, at the end of a lengthy and wide-ranging foreign select committee cross-examination, he implied she had been providing journalism training in Iran when he meant to say this was the crime for which she was being accused by the Iranians. The family initially praised his promise at the committee to try to visit her in prison in Iran, and did not criticise him.

The true culprit remains the Iranians, who – before Johnson’s blunder – had already added extra charges that threaten to put Zaghari-Ratcliffe behind bars for another five years.

But Johnson’s blunder jeopardises not just her, but also makes his own career prey to the decision of the Iranian courts. This comes as Johnson travels to Washington to persuade congressmen that the Iran nuclear deal is worth preserving. It can only be hoped that he and Britain are given a serious hearing.